Generally, solvent casting produces a part of films, such as cellulose acetate, polycarbonate and cellophane. In the solvent casting process, dope which is a polymer solution is cast from a casting die onto a casting support of belt type or drum type, stripped off after being dehumidified to some extent on the casting support, dried while being carried by a tenter machine with being held at both side edges, and further dried while being conveyed over rollers. (JP 62-46625A, JP 62-46626A, etc.).
The tenter machine includes a pin tenter and a clip tenter, and the pin tenter has a function of inserting the side edges of the web into the pins of itself by thrusting the edge of the web downward by an inserting device, such as an engaging brush. However, in conveyance of the web by a conventional pin tenter machine, the web once inserted in the pin tenters often slips off from the pin tenter thereby losing the state of being conveyed. When the speed of the conveyance increases, this phenomenon particularly becomes conspicuous and disturbs an improvement in the productivity of film forming.